Semax

What Semax is, structurally

Semax is a heptapeptide, seven residues with a free N-terminal amine and a free C-terminal acid. The synonym describes its construction: the first four residues correspond to positions four to seven of a longer natural sequence, extended at the C-terminus by Pro-Gly-Pro. That extension is a structural fact, not a statement about what it does.

The formula accounts for the sequence exactly, which is a useful check. Nine nitrogens are required and nine are present: one backbone nitrogen for each of the seven residues, plus two more from the imidazole ring of histidine. The single sulfur is the methionine thioether, the only sulfur atom in the molecule, and it is the most important atom on this page.

Two prolines sit at positions five and seven. Proline's cyclic side chain removes the backbone amide hydrogen and restricts rotation, so the C-terminal third of this peptide is conformationally stiffer than the rest. There is no cysteine, so no free thiol, no disulfide bonding and no reducing agent required.

Charge behavior is close to balanced. Glutamate contributes a negative charge and the free C-terminal acid another, while the free N-terminal amine contributes a positive one. Histidine sits in between, with an imidazole that is only partly protonated near neutral pH, which makes this peptide's net charge more pH-sensitive across the ordinary working range than a sequence carrying only strong acids and bases. Phenylalanine is the sole aromatic residue and the only appreciable hydrophobic surface. The peptide is polar and water soluble. No quantitative figure is quoted here.

Reconstitution and handling

Sterile water is the default solvent, and with no metal center to protect, PBS or an appropriate assay buffer are equally reasonable. Add diluent slowly down the vial wall, swirl rather than vortex, and let the solution clarify before use. Vortexing drives foaming and interfacial aggregation without dissolving anything faster.

Adsorption onto plasticware is worth allowing for at low concentration, since peptides bind polypropylene surfaces and a measured concentration can fall short of the prepared one. Low-protein-binding tubes reduce it. This peptide carries no strong net charge, so it has no particular affinity for charged surfaces either way.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light. Allow a cold vial to reach room temperature before opening. Reconstituted, hold at 2 to 8 degrees C for short-term work, or aliquot and freeze so no vial is thawed twice.

The weak point is unambiguous and it is the methionine. A thioether oxidizes readily to the corresponding sulfoxide on exposure to air, peroxides or trace metals, and methionine is the residue in any peptide most prone to it. Nothing else in this sequence competes: there is no cysteine to oxidize, no asparagine or glutamine to deamidate, and no aspartate to isomerize. Histidine can oxidize but far more slowly. That concentrates the handling concern on air exposure and oxidant contact rather than hydrolysis, and is the reason to prepare solutions fresh and keep headspace small.

These are storage conditions for the material, not dosing or administration guidance.

How Semax is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. Phenylalanine gives the molecule a weak absorbance near 257 nm, but a single phenylalanine is a poor chromophore for quantitation, so detection in the low UV near 214 nm, where the amide bond absorbs, remains the practical choice.

Area percent is a chromatographic measure rather than peptide content by weight. Solid-phase synthesis yields a salt, usually trifluoroacetate or acetate, and that counter-ion is outside the molecular weight above, so the mass in the vial is not all peptide. Residual trifluoroacetate, truncated chains and deletion sequences are the impurity classes chromatography should resolve.

Mass spectrometry confirms identity against the expected weight, and for this compound it carries a specific diagnostic. Methionine sulfoxide is exactly sixteen mass units heavier than methionine, so oxidation shows up as a satellite peak sixteen above the molecular ion. That peak is the direct readout of the degradation route described above, and its presence or absence says more about how the material has been handled than a purity percentage alone does.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

What does a peak sixteen mass units above the main one indicate? Oxidation of the methionine to methionine sulfoxide. Adding one oxygen atom adds sixteen to the mass, so the sulfoxide appears as a distinct satellite of the molecular ion. It is the expected oxidation product for this sequence.

Does this need protection from air as well as from light? The methionine thioether oxidizes on contact with air, peroxides or trace metal contamination, so limiting air exposure matters here more than it does for a sequence with no oxidizable residue. Small headspace, prompt resealing and freshly prepared solutions all reduce it.

Full specifications for Semax.